I elected to upgrade my 69 Arrow with Garmin 430, Stec autopilot, and
Stormscope. I love the airplane to begin with, I know what I have,
and if I fly it for 5 years I figure I get my money's work even with
50% return. Used airplanes often contain nasty surprises. I did it a
year at a time, during annual, midwinter when midwest flying weather
is grim anyway. The gradual approach also lets you learn as you go
and enjoy one new piece of equipment each year.

I believe you get better return on engine and cosmetics as long as you
don't go overboard.